Correlation of plasmids with infectivity of Borrelia burgdorferi sensu stricto type strain B31

SummaryThe prokaryotic, spirochaetal microorganism Borrelia burgdorferi is the causative agent of Lyme disease, an arthropod-borne disease of a variety of vertebrates and the most prevalent arthropod-borne disease of humans in the United States. In order to understand better the normal life cycle of B. burgdorferi, an experimental chain of infection was devised that involved multiple sequential arthropod and mammalian passages. By examining populations of B. burgdorferi emerging from different points in this infectious chain, we demonstrate that selection of B. burgdorferi populations peculiar to arthropod or vertebrate hosts is a property of at least one of the two ecologically distinct strains we examined. Distinct B. burgdorferi populations were identified using an antigenic profile, defined by a set of monoclonal antibodies to eight B. burgdorferi antigens, and a plasmid profile, defined by the naturally occurring plasmids in the starting clonal populations. These two profiles constituted the phenotypical signature of the population. In the strain exhibiting selection in the different hosts, transition from one host to another produced a striking series of alternating phenotypical signatures down the chain of infection. At the molecular level, the alternating signatures were manifested as a reciprocal relationship between the expression of certain antigenic forms of outer surface protein (Osp) B and OspC. In the case of OspC, the antigenic changes could be correlated to the presence of one of two distinctly different alleles of the ospC gene in a full-length and presumably transcriptionally active state. In the case of OspB, two alleles were again identified. However, their differences were minor and their relationship to OspB antigenic variation more complicated. In addition to the reciprocating changes in the antigenic profile, a reciprocating change in the size (probably the multimeric state) of a 9.0 kbp supercoiled plasmid was also noted. Selection of distinct populations in the tick may be responsible for the microorganism's ability to infect a wide range of vertebrate hosts efficiently, in that the tick might provide selective pressure for the elimination of the population selected in the previous host.

Section: Discussionmentioning

confidence: 95%

An experimental chain of infection reveals that distinct Borrelia burgdorferi populations are selected in arthropod and mammalian hosts

Ryan

Levine

Apperson

et al. 1998

“…The relative mobility of the two reactive bands detected from strain B31-CH3 (Fig. 1B, lane 1) suggested that they corresponded to the 28 kb and 54 kb linear plasmids lp28-1 and lp54 respectively (Barbour, 1991;Xu et al, 1996;Fraser et al, 1997). Only one plasmid, lp54, was detected in strain B31-CH100 (Fig.…”

Section: Rna Subtraction and Southern Analysis Using Subtractive Probesmentioning

confidence: 95%

Increased expression of Borrelia burgdorferi vlsE in response to human endothelial cell membranes

Hudson

Frye

Quinn

et al. 2001

RNA isolated from virulent Borrelia burgdorferi cells incubated with human endothelial or neurological tissue cells was subjected to subtractive hybridization using RNA from the same strain incubated in tissue culture medium alone. This RNA subtractive technique generated specific probes that hybridized to two restriction fragments (8.2 kb and 10 kb respectively) generated by EcoRI digestion of total plasmid DNA. The 10 kb EcoRI fragment localized to lp28‐1 and was subsequently identified as the variable membrane protein‐like sequence (vls) region, which includes an expression locus (vlsE) and 15 silent cassettes. vlsE encodes a 36 kDa outer surface protein that undergoes antigenic variation during animal infections. Primer extension analysis identified the 5′ end of a transcript and a putative promoter for vlsE. Quantitative reverse transcription–polymerase chain reaction (RT–PCR) suggested that the expression of vlsE increased when virulent B. burgdorferi cells were incubated with human tissue cells or purified cell membranes isolated from those same cell lines. A 138 bp region upstream of the vlsE region that was not reported in the genome sequence was sequenced using specific 32P end‐labelled primers in a DNA cycle sequencing system at high annealing temperatures. Analysis revealed that it contained a 51 bp inverted repeat, which could form an extremely stable cruciform structure. Southern blots probed with the vlsE promoter/operator region indicated that part or all of this sequence could be found on other B. burgdorferi plasmids.

“…After the isolation of clone 4a from a solid agar colony, passage through a BALB/c mouse for 4 weeks and re-isolation from the mouse (see Casjens et al, 1997a), it carried all of the plasmids whose sequences are known except for cp9, lp5, lp28-3 and lp28-4 (data not shown). The plasmids missing in clone 4a may well have been lost during the cloning/mouse passage procedure because Borrelia strains have often been found to lose one or more plasmids during laboratory propagation and cloning procedures (for example Barbour, 1988;Schwan et al, 1988;Persing et al, 1994;Norris et al, 1995;Xu et al, 1996).…”

Section: Twenty-two Replicons In One Bacterium?mentioning

confidence: 99%

“…The linear DNAs have covalently closed hairpin telomeres (Barbour and Garon, 1987;Hinnebusch et al, 1990;Hinnebusch and Barbour, 1991;Casjens et al, 1997b;Fraser et al, 1997). Most of the plasmids can be lost and are not required for propagation of the bacteria in culture, but loss of infectivity in mice often parallels plasmid loss (for example Barbour, 1988;Hyde and Johnson, 1988;Schwan et al, 1988;Norris et al, 1992;Sadziene et al, 1993b;Persing et al, 1994;Xu et al, 1996;Zhang et al, 1997; but see Casjens et al, 1997a). For brevity, we will refer to the Borrelia extrachromosomal DNA elements as`plasmids', even though some of them may be universally present and are probably essential in nature (see Marconi et al, 1996a;Casjens et al, 1997b;Tilly et al, 1997), carry genes that may be metabolically important (Margolis et al, 1994) or have never been lost in culture.…”

Section: Introductionmentioning

confidence: 99%

A bacterial genome in flux: the twelve linear and nine circular extrachromosomal DNAs in an infectious isolate of the Lyme disease spirochete Borrelia burgdorferi

Casjens

Palmer

Vugt

et al. 2000

757

1,241

We have determined that Borrelia burgdorferi strain B31 MI carries 21 extrachromosomal DNA elements, the largest number known for any bacterium. Among these are 12 linear and nine circular plasmids, whose sequences total 610 694 bp. We report here the nucleotide sequence of three linear and seven circular plasmids (comprising 290 546 bp) in this infectious isolate. This completes the genome sequencing project for this organism; its genome size is 1 521 419 bp (plus about 2000 bp of undetermined telomeric sequences). Analysis of the sequence implies that there has been extensive and sometimes rather recent DNA rearrangement among a number of the linear plasmids. Many of these events appear to have been mediated by recombinational processes that formed duplications. These many regions of similarity are reflected in the fact that most plasmid genes are members of one of the genome's 161 paralogous gene families; 107 of these gene families, which vary in size from two to 41 members, contain at least one plasmid gene. These rearrangements appear to have contributed to a surprisingly large number of apparently non‐functional pseudogenes, a very unusual feature for a prokaryotic genome. The presence of these damaged genes suggests that some of the plasmids may be in a period of rapid evolution. The sequence predicts 535 plasmid genes ≥300 bp in length that may be intact and 167 apparently mutationally damaged and/or unexpressed genes (pseudogenes). The large majority, over 90%, of genes on these plasmids have no convincing similarity to genes outside Borrelia, suggesting that they perform specialized functions.